Selectivity control



Filed Dec. 2, 1936 lYwvwtoP: James. BB@ s,

is Attofrw ey.

Patented Oct. 11, 1938 UNITED STATES SELECTIVITY CONTROL James E. Beggs, Schenectady, N.Y., yassignor to' General Electric New York Company, `a corporation of Application Decemberrz, 193s, serial No. 113,866

3 Claims.

My invention relates to radio receiving apparatus and particularly to such apparatusvwhich is provided with selectivity control. Many forms of such apparatus as heretofore proposed have been subject to the objection that each time the apparatus is tuned to a different station it yhas been necessary in order to obtain proper tuning for the operator to actuate some -device to change the apparatus from a condition of high delity to one of high selectivity, then after tuning is completed to change it back to a condition of the desired higher fidelity.

It is the object of my invention to provide improved apparatus of this character by which this objection is overcome.

In accordance with my invention I have provided radio receiving apparatus having means for varying the selectivity thereof and having a tuning device adapted to be actuated by the hand of the operator, the arrangement being such that the conductivity of the hand of the operator on the device functions to cause the desired increase in the selectivity; likewise the removal of the hand of the operator from the device causes a restoration of the original selectivity.

My invention will be understood from the following description taken in connection with the accompanying drawing, and its scope will be pointed out vin the appended claims.

In the single figure of the drawing, which is a circuit diagram illustrating my invention which is shown as forming a part of a superheterodyne radio receiving system, I is the antenna or pickup device, 2 is the radio frequency amplifier stage, 3 is the detector and oscillator stage, 4 is the stage of intermediate frequency amplification, 5 is the second detector and automatic volume control stage, I is the audio amplifier, and 'I is the loudspeaker. The detector and oscillator stage 3 is shown coupled to the intermediate frequency amplifier stage 4 by the coupling transformer I0 having the primary winding I I and the secondary winding I2 tuned to the intermediate frequency by the adjustable capacitors I3 and I4 respectively. The primary and secondary windings II and I2 are wound in the same direction on the same axes, the windings being normally somewhat loosely coupled whereby a relatively high degree of selectivity results in which condition 50 the apparatus is well adapted to be accurately tuned to a desired carrier.

In order that the apparatus may exhibit greater delity than that obtained with its natural high selectivity, I have shown means, now to be described, for increasing the effective coupling between `the primary and secondary windings of thetransformer. This vmeans comprises` the phase shifting network I6 including the capacitor Il' and theresistor I8 4connected in series'between the upperend of the secondary winding -I2 and vground through the bypass capacitor I9 The impedance of the capacitor Il is large'with respectv to that of the resistor I8 at the intermediate frequency employed so that the currenty in the resistor I8 and hence the, voltage across the resistor is nearly ahead ofthe voltage across the secondary winding I2. This phase displaced voltage is amplified by the electronl discharge amplifier L2l! and appliedto the primary winding I I to produce an effective increase in the coupling ofi the transformer." l

For the above-mentioned amplification of the phase displaced voltage in the resistor I8 a point of the network I6 intermediate the capacitor and the resistor connects by the conductor 2Iwith the grid 22 of the amplifier 20 and the anode 23 connects by the conductor 24 with the upper end of primary winding II, the lower end of which connects with ground through'the bypass capacitor 25. The cathode 26 of the amplier 20 connects with a source of voltage, not shown, which, for example, may be plus l0 Volts.

The apparatus is provided with a special form of hand operated tuning device, or knob, which for example may be like that shown at 30. The knob 30 which may be of insulating material preferably has the two metallic rings 3l and 32 embedded therein but insulated from each other which rings are adapted to be connected together by the ngers of the operator when the knob is turned for changing the tuning of the apparatus. Ring 32 connects with ground and ring 3l connects through the resistor 33 with the lower end of the resistor I8. A positive voltage is supplied to the ring SI and through the resistor 33 to the lower end of the resistor I8 by means of the potentiometer 34. one end of which is represented as being at a potential of plus 3 volts and the other end at a potential of plus 8 volts, the movable arm ofthe potentiometer including the resistor 35.

In the normal use of the apparatus at vwhich time the hand of the operator is not in contact with the tuning knob 30, a positive voltage is supplied to the grid 22 of the amplifier 2U through the resistor I8 of the phase shifting network such that the amplified phase displaced Voltage from that network is supplied to the primary I I to produce an increase in the coupling of the transformer I0 to give the desired degree of delity. When, however, the operator grasps the tuning knob 3B to change the tuning of the apparatus, for example to receive signals from a different station, the presence of his fingers on the tuning knob in a position connecting the rings 3| and 32 thereof reduces the voltage applied by the potentiometer to the gri-d 22 of the amplifier 20 to a value sufciently negative with respect to the cathode 26 so as to out oiT the amplifier or reduce its output to a negligible value. Thus while the knob 30 is being turned by the operator to tune the apparatus, there is little or no phase displaced voltage supplied to the primary Il and accordingly the coupling of the transformer automatically returns to its original loose condition at which the selectivity of the apparatus is relatively high. Upon removal of the iingers from the tuning knob the amplifier 20 again becomes operative and the resulting eiective increase in coupling of the transformer I restores the fidelity of the apparatus although at some expense of selectivity.

In the drawing I have shown the amplifier 4 connected with the second detector stage 5 through the coupling transformer I0 which may be similar to that shown at I0. `The primary of this transformer also may be supplied with a phase displaced voltage from the phase shifting network I6' similar to that shown at I6 and amplified by the amplier 20 which is similar to that shown at 20. Since the transformer I0', the phase shifting network I6', and amplifier 20' are like the corresponding parts already described, a detail description thereof seems to be unnecessary and will not be made.

I have chosen the particular embodiment described above as illustrative of my invention and it will be apparent that various modifications may be made without departing from the spirit and scope of my invention which modications I aim to cover by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Radio receiving apparatus provided with a hand operated tuning knob, said knob having normally insulated conducting portions arranged to be touched simultaneously by the hand of the operator when changing the tuning of the apparatus and means responsive to the simultaneous touching of said portions by the hand of the operator for increasing the selectivity of the apparatus.

2. Radio receiving apparatus provided with a hand operated tuning knob, said knob having spaced conducting portions insulated from each other and arranged to be bridged by the hand of an operator, means for causing said apparatus to have a predetermined degree of selectivity and means controlled by the bridging of said conduct- Aing portions by the hand of the operator for increasing the selectivity oi said apparatus.

3. Radio receiving apparatus including a coupling transformer and a hand operated tuning knob constructed of insulating material and having spaced conducting portions arranged to be bridged by the hand of an operator, means operative to increase the effective coupling of said transformer and means controlled by the bridging of said conducting portions by the hand of the operator for rendering said means inoperative.

JAMES E. BEGGS. 

